High-frequency electronic apparatus for heating dielectric materials



April 26, 1949. J, JOY 2,468,263

HIGH-FREQUENCY ELECTRONIC APPARATUS FOR HEATING DIELECTRIC MATERIALS Filed March 51, 1945 INVENTOR. .JOSEPH E. JOY

CQM

ATTORNEY Patented Apr. 26, 1949 HIGH-FREQUENCY ELECTRONIC APPARA- TUS FOB. HEATING DIELECTRIC MATE RIALS Joseph E. Joy, Collingswood; N. J'., assignor to Radio Corporation of America, vacorporation-of Delaware Application March 31, 1945, Serial No; 586,003

8 Claims. 1

This invention relates to electronic heating apparatus, and more particularly to apparatus employing high frequenc electric energy for heating dielectric materials by reason of dielectric losses produced therein, the present invention having particular relation to the type of apparatus disclosedv and claimed in the copending application of Cyril N. Hoyler, Serial No. 539,855, filed June 12, 1944, and assigned to Radio C'orporation of America.

In the aforesaid copending application there is disclosed apparatus for bonding together a plurality of superposed layers of dielectric, thermoplastic material'by passing overlapping portions of the layers between two electrodes connected to asource of high frequency, electric energy. The high frequency electric field established between the electrodes serves to quickly heat the dielectricmaterial to' the plasticating or fusion temperature thereof. Pressure applied to the several layers while" hot serves to unite the layers into an integral unit.

Commercial apparatus of this type has been constructed in a form similar to conventional sewing machines and has included (1) a grounded metallic bedplate-for supporting the work, (2) a head or frame supported by the bedplate, (3) a pairof roller electrodes, one mounted below the bedplate and extending through an opening therein, and the other carried by the aforesaid head in alignment with the first mentioned roller for cooperation therewith, and (4) a high frequency oscillation generator having a grounded output terminal and a second terminal the potential of which'varies with respect to ground; The electrode roller mounted below the bedplate is connected to the last mentioned terminal of the generator while the other roller is connected to ground through the machine head.

In order to accommodate workpieces of substantial width, it is necessary to make the machine head fairly long between the point where it supports the upper electrode roller and its point of connection to the bedplate. The length of the head is then large compared to the wave length at the operating frequency of the generator and, due to the high impedance afforded thereby, there is set up in the head a standing wave of-voltage which not only results in instability and erratic operation, but also some degree of danger to the operator.

The primary object of my present invention-is to provide an improved electronic heating, apparatus of thetype set forth'above which will not be. subject tov the aforementioned disadvantageof similar prior art apparatus.

More particularly, it is an object of my present invention to provid'ean improved relectronic heating apparatus for heating dielectric materials which will'accommodateworkpieces of all widths- Withinthe limits of the apparatus and which will; atthefsame time, be'entir'ely stableandhniform" in. operation, as wellas safe for the operator'td use.-

Another'object of. my. present invention is to provide an improvement; in apparatus-of the type set forth, which can-be readily 'appl-iedto'exlsting electronic heating and/or bonding machineswith great ease, thereby rendering such machines free fromthe objection pointed out heretofore.

It is also. an object of my present invention to provide'an improved apparatus as aforesaid which is economical in cost. and highly'efiicient in-use.

In accordance with my present invention, I

provide'an.electro-conductive plate of substantial area around or in close proximity to'the upper elect-rode'roller (that is, theone intended to'be atground potential) and dispose this plate in close Thus,

proximity also to thegrounded bedplate. the'plate which I add to the'apparatus cooperates with the bedplate to-form, atthe' operating-ire quency, a low impedance capacitor in shunt rela tion with the'machine head between the assoelated-electrode roller and-ground. This permits the current to pass off and hence eliminatesthe standing wave-which normally results along the-- head, with attendant safety and improved, uni-' form, stable operation regardless of the WidtIlOf the material presented to the machine.

The novel features that Iconsider characteristic of my, invention are set forth with particu larity in the appended claims. The invention it self, however, both as to its organization and method of operation, as well as additional objects and advantages thereof, will best be understoodfrom the following description of one embodiment thereof, when'readdn connection with the cuit of the oscillation'generator according to my present invention.

Referring more particularly to the drawing, wherein similar reference characters designate corresponding'parts throughout, there is-shown an electronic heating machine for heating dielectrio materials, the machine including a metallic bedplate I provided with an opening 3 and a slot 5. The bedplate I serves to support a workpiece I shown in the drawing as a pair of thermoplastic layers of dielectric material arranged in overlapping relation along adjacent marginal portions at which they are to be bonded together between a pair of cooperating rollers 9 and II. The bedplate I is maintained at ground potential by connection to any suitable ground point I3.

Secured to the grounded bedplate l in electro-conductive relation therewith is a hollow head I5, also of electro-conductive material, the head l5 terminating in a downwardly extending arm I5a which is spaced from the bedplate I and in which the roller 9 is mounted for vertical adjustment. For the latter purpose, the roller 9 is secured to a shaft I7 which is rotatably carried by a yoke I9. Secured to the yoke I9 is a bracket 2! which carries a vertical shaft 23 slidable vertically in and splined to a hollow shaft 25 Within the arm I511. The yoke I9 also carries a post 2? which extends through a vertical slot 29 in one side of the arm I5a. By manipulating the post 21 manually within the slot 29, the assembly comprising the roller 9, the yoke I9, the bracket 2i, the shaft 23 and a pair of bevel gears 3i which couple the shafts H and 23 to each other may be raised or lowered as a unit relative to the bedplate I and the roller II. When the rollers 9 and II are separated, the workpiece 'I may be inserted therebetween, after which the roller 9 is lowered onto the work.

The shaft 25 is coupled by a pair of bevel gears 33 to a shaft 35 within the head I5. A motor 9? carried by the head I5 drives the shaft which, in turn, delivers power to the shafts 25, 23 and I I for driving the upper roller 9. The lower roller I I, which is rotatably supported on a shaft 39 below the bedplate I in electrically insulated relation thereto and which extends through the opening 3 into cooperative relation with the roller 9, may also be driven by suitable coupling means (not shown) from the motor 9?. Thus, as the rollers 9 and I I rotate while engaging the workpiece I, they advance the workpiece between them.

For supplying electrical energy to the rollers 9 and II, there is provided a suitable, high frequency oscillation generator ll, such as a vacuum tube oscillator operating at radio frequency. One terminal of the oscillator II is connected to the ground point I3 by the outer conductor d3 of a concentrictransmission line. The other terminal of the oscillator is connected to the lower roller II by means of the inner conductor 95 of the aforesaid transmission line and a brush or wiper 41. A tuning capacitor comprising a metallic cylinder 49 carried by the conductor 35 and a metallic sleeve 5I which surrounds the cylinder 49 in spaced relation thereto and which is slidably mounted in a. metallic tube 53 conductively supported by the bedplate l and through which the bedplate I may be connected to the ground point I3, if desired, serves to tune the circuit. The capacitance of the capacitor t9, El may be varied manually to tune the circuit for loads of difierent thicknesses between: the roller electrodes 9 and II by means of a post 55 secured to the capacitor sleeve 5i and extending through a slot 57 in alignment with the slot 5. Energy supplied to the electrodes 9 and I I establishes a radio frequency electric field therebetween and, since the overlapping portions of the workpiece I are trio 1 s 9 and II or by other suitable means in a manner more fully set forth in the above identified, copending, Hoyler application.

Where the workpiece l is quite wide, it is apparent that the l5 must be made quite long between its arm Ida and its arm or base I522 where it is connected to the bedplate I if the machine is to accommodate the work. In such case, the length of the electrical path through the head It; becomes large compared to the wave length at operating frequency of the oscillator ll. ce this path has a high impedance at the operfrequency, a standing wave is set up in the d It which in voltage between the ground point E3 and the roller electrode 9. Thus, the roller 9, instead of being at ground potential, actually at some other potential. This not only results in unstable operation of the machine, but also creates a somewhat dangerous condition for the operator.

To eliminate the standing wave, I mount on the lower end of the ltd an electro-conductive plate ill. The plate El should have a substantial area may be mounted either to one side of the roller in close proximity thereto, as shown in the drawing, or it may be arranged to straddle the roller 8. In any case, it is mounted close to the grounded bedplate l and cooperates therewith to provide a low impedance path between the roller ii and the ground point 13 through which the high frequency current can readily return to ground. This low impedance path, it will be noted, is arranged in shunt relation with the head It. In this way, the standing wave in the head I5 and its attendant disadvantages are entirely eliminated.

Although I have shown and described but one embodiment of my invention, it will undoubtedly be apparent to those skilled in the art that other modifications and forms thereof are possible. I th refore desire that my invention shall not be limited except insofar as is made necessary by the prior art and by the spirit of the appended claims.

I claim as my invention:

1. In electronic heating apparatus for heating a dielectric workpiece, the combination of a pair of spaced, cooperating electrodes, a source of high frequency electric energy having a pair of output members one of which is maintained at a reference potential and the other at a potential which varies with respect to said reference potential, means coupling said electrodes each to a separate one or said output members, said coupling means having a length which is long compared to the wave length at high frequency, said coupling means being so terminated at said electrodes that there tends to be set up'in the path between that one of said electrodes which is coupled to said reference potential output member and said last named output member a standing voltage wave which would cause said last named electrode to have a voltage thereon other'than at said reference potential, and low impedance means connecting said last named electrode to a point at said reference potential for providing a low impedance path between said last named electrode and said point whereby to eliminate said standing wave.

2. The invention set'forth in claim I wherein 1e aid of pressure applied to the Work by" said low impedance means comprises a reactive element.

3. 'The invention set'forth in claim 1 wherein said low impedance means comprises a capacitor.

4. In electronic heating apparatus for heating a dielectric workpiece, the combination of a pair of spaced electrodes adapted to receive said workpiece therebetween, a source of high frequency electric energy having a pair of output members one of which is maintained at ground potential and the other at a potential which varies with respect to ground potential, means coupling said electrodes each to a separate one of saidoutput members, said coupling means havinga length which is long compared to the wave length at said high frequency, said coupling means being so terminated at said electrodes that there tends to be set up in the path between that one of said electrodes which is coupled to said grounded output member and ground a standing wave of voltage at said frequency which would cause said last named electrode to have a voltage thereon other than at ground potential, and a low impedance capacitor connected between said last named electrode and ground in shunt with that portion of said path in which said standing wave tends to exist whereby to eliminate said standing wave and bring the voltage on said last named electrode to ground potential.

5. In electronic apparatus for heating a dielectric workpiece, the combination of an electroconductive bedplate adapted to support said workpiece, said bedplate being maintained at ground potential, a pair of spaced electrodes associated with said bedplate in spaced relation to each other for receiving said workpiece therebetween, a source of high frequency electric energy having a pair of output members one of which is also maintained at ground potential and the other of which is maintained at a potential which varies with respect to ground potential, means coupling said electrodes each to a separate one of said output members, said coupling means having a length which is long compared to the wave length at said high frequency, said coupling means being so terminated at said electrodes that there tends to be set up in the path between that one of said electrodes which is coupled to said grounded output member and ground a standing wave of voltage at said frequency which would cause said last named electrode to have a voltage thereon other than at ground potential, and an electro-conductive plate mounted in close proximity to said last named electrode and in closely spaced relation to said bedplate, said plate and bedplate cooperating to provide a low impedance capacitor in shunt with that portion of said path in which said standing wave tends to exist for eliminating said standing wave and bringing the voltage on said last named electrode to ground potential.

6. In electrical apparatus for heating a dielectric workpiece, the combination of an electroconductive bedplate adapted to support said workpiece and having an opening therein, said bedplate being maintained at ground potential, a pair of electro-conductive rollers arranged for peripheral cooperation and constituting electrodes adapted to receive said workpiece therebetween, one of said rollers being disposed on one side of said bedplate and the other on the opposite side thereof, said other roller eXtending through said opening into cooperative relation with said first mentioned roller, a source of high frequency electric energy having a pair of output members one of which is also maintained at groundpotential and the other of which is maintained at a potential which varies with respect to ground potential, means coupling said first mentioned roller to said grounded output member and said other roller to said other output member, said coupling means having a path len th'between said grounded output member and said first mentioned roller which is long compared tothe wave length at said high frequency, said coupling means being so terminated at said electrodes that there tends to be set up-in said path. length a standing wave of voltage at said frequency which would cause said first mentioned roller to have a voltage thereon other than at ground potential, and an electro-conductive plate mounted in close proximity to said first mentionedroller and in closely spaced relation to said bedplate, said plate and bedplate cooperating to provide a low impedance capacitor in shunt with said path length for eliminating said standing wave and bringing the voltage on said first mentioned roller to ground potential.

7. In electrical apparatus for heating a dielectric workpiece, the combination of an electroconductive bedplate adapted to support said workpiece and having an opening therein, said bedplate being maintained at ground potential, a pair of electro-conductive rollers arranged for peripheral cooperation and constituting electrodes adapted to receive said workpiece therebetween, an elongated, electro-conductive head carried by said bedplate on one side thereof and extending to a point over said opening, one of said rollers being rotatably carried by said head in alignment with said opening, means rotatably mounting the other of said rollers on the opposite side of said bedplate, said other roller extending through said opening into cooperative relation with said first mentioned roller, a source of high frequency electric energy having a pair of output members one of which is also maintained at ground potential and the other of which is maintained at a potential which varies with respect to ground potential, means coupling said other roller to said other output member, said head serving to connect said first mentioned roller to ground but having a length between its connection to said grounded bedplate and said first mentioned roller which is long compared to the wave length at said high frequency, said head having such an impedance at said high frequency that there tends to be set up in said head a standing wave of voltage at said frequency which would cause said first mentioned roller to have a voltage thereon other than at ground potential, and an electro-conductive plate carried by said head in close proximity to said first mentioned roller and in closely spaced relation to said bedplate, said plate and bedplate cooperating to provide a low impedance capacitor between said first mentioned roller and said bedplate in shunt relation with said head for eliminating said standing wave and bringing the voltage on said first mentioned roller to ground potential.

8. In electronic heating apparatus for heating a dielectric workpiece, the combination of a pair of spaced, cooperating electrodes, a source of high frequency electric energy having a pair of output members one of which is maintained at a reference potential and the other at a potential which varies with respect to said reference potential, means coupling said electrodes each to a separate one of said output members, said coupling means including in the portion thereof which couples said reference potential output member and that one of said electrodes which is coupled to said last named output member a member which is long compared to the wave length at said high frequency and which has a relatively high impedance at said high frequency whereby there tends to be set up along said high impedance member a standing voltage Wave which would cause said last named electrode to have a voltage thereon other than at said reference potential, and low impedance means connecting said last named electrode to a point at said reference potential for providing a low impedance path between said last named electrode and said point whereby to eliminate said standing wave.

JOSEPH E. JOY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Name Date Bierwirth Jan. 12, 1943 Number OTHER REFERENCES 

